Public concern about the potential effects of endocrine disrupting chemicals (EDCs) on human health has heightened the need for research that assesses the mechanistic effects of exposure to these chemicals. EDC exposure during critical periods of development can result in irreversible changes in tissue differentiation alterig the sex and long-term reproductive potential of offspring supporting a developmental origin of these later lifespan impacts. The later lifespan impacts in many studies are attributed to epigenetic changes in the genome. While a number of studies have focused on DNA methylation as an epigenetic mechanism of toxicity, few studies have investigated the role of microRNAs (miRNAs). miRNAs are small RNAs that regulate expression of genes and proteins. miRNAs play a role in neuroendocrine and reproductive function and disease and are altered following chemical exposure in toxicology studies, but have yet to be investigated as an epigenetic mechanism of atrazine (ATR) toxicity. ATR is an agricultural herbicide commonly reported to contaminate drinking water supplies throughout the United States. ATR is implicated as an endocrine disruptor and a potential carcinogen. ATR is reported to act upon the hypothalamus-pituitary-gonadal (HPG) axis, but the endocrine disrupting properties of ATR are not completely understood. In our ongoing study, transcriptomic analysis immediately following a developmental ATR exposure from 1 to 72 hours post fertilization (hpf) in the zebrafish model system supports alterations in the HPG axis and neuroendocrine control of ATR endocrine disruption alterations. Furthermore, adult zebrafish developmentally exposed to ATR and allowed to mature under normal laboratory conditions exhibited significant alterations in life history traits and reproductive function. Our central hypothesis is that alterations in the HPG axi from a developmental ATR exposure are driven by epigenetic mechanisms. In addition, we hypothesize that ATR endocrine disruption alterations are under neuroendocrine control. The long term goal of our study is to define and link the genetic and epigenetic mechanisms governing the developmental origin of ATR-induced alterations on the HPG axis. In this study we will first identify miRNA expression alterations immediately following a developmental ATR exposure to define epigenetic targets of ATR toxicity. In the second and third aims, we will perform comparative transcriptomic analysis of brain/pituitary and gonadal tissue isolated from adult female and male zebrafish developmentally exposed to ATR. Preliminary transcriptomic data with adult zebrafish brain tissue further supports alterations in HPG signaling. A multitude of confirmation and targeted assays will also be performed to further investigate mechanisms of ATR toxicity on the HPG axis. The data collected in aims 2 and 3 will be coupled to that of aim 1 to link genetic and epigenetic mechanisms of the developmental origin of ATR-induced alterations to the HPG axis. Moreover, throughout this study graduate and undergraduate students will play an active role and gain extensive experience in all aspects of conducting a scientific research study.